However, I initially couldn't reproduce it, and after spending a few hours with pgfplots I wanted my own style anyway.

But first, a recap:
Once you've completely left office-like wordprocessors behinds and fully embraced the wonder of typesetting in LaTeX you find yourself wanting to produce more and more of the figures directly in latex, rather than simply importing figures.

pgfplots is not meant for drawing potential energy diagrammes, but it can be made to do it -- it's 'dum' in the sense that it's not aware of what a PE diagram is, so you'll have to draw all objects expliticly. In the end, it's actually quite simple though.